The molecular mechanism of stimulation of cell proliferation and the alterations which occur in chemically transformed cells will be explored in this project. Preliminary data from this laboratory and other data suggest that synthesis of specific messenger RNA sequences encoding for proteins necessary for stimulation of DNA synthesis and proliferation is necessary in quiescent nontransformed cells, but remain expressed in resting chemically transformed cells. This hypothesis (and alternate possibilities) will be tested in this project through the use of cell culture model systems which include the nontransformed AKR-2B and C3H/10T 1/2 cell lines and chemically transformed derivative clones (AKR-MCA and C3H/MCA-58). Emphasis will be placed on the study of cells in the quiescent, nonproliferating state and in the prereplicative interval between the stimulation to proliferate at the onset of DNA synthesis. These specific experiments will include: (1) an analysis of the mechanism by which alpha-amanitin inhibits stimulation of DNA synthesis in nontransformed cells by examining the effect of varying concentrations of alpha-amanitin administered to intact cells on the accumulation of heterogeneous nuclear RNA and mRNA in whole cells, the DNA directed RNA polymerase type II activity in isolated nuclei, and the relative number of total cellular RNA polymerase II molecules bound by alpha-amanitin; (2) an analysis of messenger RNA sequences which characterize resting cells and cells in the prereplicative interval with the isolation of "growth specific" complementary DNA probes; and (3) utilization of the "growth specific" cDNA probe to determine the subcellular distribution of those sequences in resting and stimulated nontransformed and cells.